A non-Contact Electro-optical Displacement follower measures displacement by electrically processing a target image of the part under test which has been captured optically and converted into an electrical image. As this kind of equipment can measure displacement without actually coming into contact with the object being measured, one can measure high speed displacement, microscopic displacement, etc. from a set distance accurately, without having any effect upon the operation of the part which is displaced. The equipment can thus be used in various fields, such as research, experiment, manufacturing, test, etc., because of its ability to measure the displacement by merely capturing the displacement part optically without obstructing the operating state, no matter what the shape of the displaced part.
Concerning conventional non-contact electro-optical displacement followers, it was often necessary to move the target or the measuring equipment (camera) when for some reason the optical image of the part under test had to be moved beyond the range within which the above image was captured and that measurement or adjustment could be carried out. However, in general, neither could be easily moved without disrupting the experiment, as the part to be measured would easily fall out of sight. It is very time consuming to move a camera each time the displacement measurement the purpose of which is to measure microscopic movements is carried out. Moreover, it becomes difficult to obtain the measurement data maintaining the reliability and reproducibility and it is against the demand of quick and precise displacement measurement.
The most conventional equipment used an analog output to display the amount of displacement e.g. moving coil meter. With this system there was no way to display a warning to inform when the target's light/dark boundary was out of the measurable field even by a small amount. This was because the measurable field of the equipment was often small in proportion to the field which optically captures the light/dark target which is the device under test. In order to compensate for this defect, a system was adapted that connects the system in parallel, to an oscilloscope, and confirms the signal from the measuring equipment on a CRT. However, using this method, it is impossible to confirm whether the relative deflection between the target and the measuring equipment is beyond the fixed range or not. Also when using this kind of displacement follower, the measurement mode needs to be set up, according to the amount of light/dark of the target. If this is not set up correctly, measurement can not be carried out, because there will be an incorrect operating display.
In this case, the operator is forced to manually view the target, or change the mode setting by sighting again the target. In equipment used to measure the microscopic or short time displacement, conditions which require a lot of readjusting of the camera should be avoided, as well as those where individual operators ability will make a difference in the results.
When carrying out non-contact electro-optical displacement measurements, one must set up the target properly. Also displacement can not be measured accurately unless each operational step such as setting of camera and other measuring equipments, initial adjustment and the following modifications are carried out carefully, and meticulously. Accuracy naturally depends on how well the system has been initially set up, and subsequently, how carefully the modification operations are carried out. This was regarded as being complicated for beginners, since these operations required skill and intuition due to their complex construction and operating requirements. This was especially true when other measurement equipment or optional functions such as operation processing equipment was added to it.
In displacement measurement using the non-contact electro-optical displacement follower, there was sometimes the problem that the change of the position of light emitted or reflected from the target was taken as change of position of the target. Brightness caused the target to change its amount of reflection, and the deflection current inside the measuring equipment would automatically compensate for this change. This decreased the accuracy, as the read out would indicate that displacement had occurred. Accordingly the best way to perform an accurate displacement measurement is to irradiate a constant source of illumination on the target and make sure not to change the brightness of the target. This did not solve the problem of what to do to compensate for this problem when measuring outdoors, or when measuring large units, because it was impossible to disregard the amount of sunshine or the presence of interference light.
To eliminate this problem, what is known as the "Light Servo system" came into use. The system can detect any change of light, and subsequently compensate for this in the measurement results, thus allowing accurate measurement of displacement.
The Light Servo System forms a "Servo Loop Circuit" which changes the high voltage for electron acceleration according to the quantity of incident light using a photoelectric conversion system, and subsequently accounts for the influence of the interference light. However, the high voltage power supply can only maintain the output voltage constant and thus the frequency response of the servo system is apt to be low. The system is effective only when there is influence from light whose period of variation is relatively long (e.g. influence of daylight on displacement measurement over a long period of time). However it is then ineffective in cases where the light cycles are changing at high-speed. e.g. Flickering Light in the case of electric discharge lamps operated at main power supply frequency.
The main purpose of this invention is to provide a non-contact electro-optical displacement follower, which can move the target image electromagnetically in an optional way to compensate for target movement and re-measure the displaced target by re-adjusting the system quickly and easily.
The invention also enables one to make a non-contact electro-optical displacement follower which displays the relationship between the target and equipment, thus, the conditions of measurement and the field of view.
Moreover the system also allows the taking of high-accuracy measurements, without requiring a particularly high level of skill or intuition.
Most of all, the Light Servo System was devised to allow for the accurate measurement of displacement in situations where there is high-speed changing interference light (such as a series of electrical discharges).